The communications-based train control system (CBTC) has become the trend for development of train control system in rail transit. CBTC introduces communication subsystem into the system and establishes continuous, two-way and high speed onboard-wayside communication. In this way, the command and state of a train can be reliably exchanged between the train and the wayside equipment, and hence the major CBTC wayside equipment and the controlled object (train) can be reliably and effectively connected. A safe interval between trains can be ensured based on precise train-positioning.
Specifically, the term “movement authority (MA)” refers to a part of line from the rear of a train to a front obstacle served as the terminal point, and the term “end of movement authority” refers to the target point which the train cannot overtakes under any circumstance. A schematic diagram of the movement authority according to the prior art is shown in FIG. 1. In a CBTC system, a zone controller subsystem determines the running direction and movement authority of a train according to the route information, track data and temporary speed restriction information, etc. provided by interlocking subsystems. The zone controller subsystem also ensures a safe interval between the leading train and the following train so as to meet the requirements for designed operation interval and turn-back interval. It continuously sends necessary information of speed, distance and track state, etc. to onboard equipments, or transmits information of operation authority of a train to onboard equipments, so as to enable the onboard equipments to determine the safety speed restriction for train operation. This ensures a safe interval between trains and prevents from over-speed.
In the present urban rail transit, certain defects still exist when realizing train tracking, although wireless communication has been used to carry out onboard-wayside information exchange.
In the control system of urban rail transit abroad, the equipments used for measuring the secondary track occupation can be classified as the multi-information track circuit, the digital track circuit and the axle counter.
In the control system using multi-information track circuit and digital track circuit, the speed of a train follows a speed level. FIG. 2 shows a schematic view of train tracking following the speed level according to the prior art; wherein the curved line represents the movement authority of a train, with the tracking interval determined by the resolution of the track circuit section. Such resolution is a block section, and the lower the resolution is, the shorter the interval for train operation will be. However, the length of track circuit sections is relatively longer in practical, generally more than 600 meters, which has considerably influenced the operation efficiency.
In a system that combines the wireless communication with track sections/track circuits, as comparison, the physical sections, i.e. the track sections/track circuits, are logically subdivided into a plurality of virtual sections, so that the train tracking can be realized on the basis of train-positioning with a virtual section as a unit. The speed of the train follows a segmental curve with a relatively higher resolution. FIG. 3 shows a schematic view of train tracking following the segmental curve according to the prior art, wherein the curved line represents the movement authority of a train; the virtual sections are subsets of the block sections.
Comparing with the block sections, the length of the virtual sections is shorter, generally about 50 meters, and the tracking interval between trains is smaller.
Comparing with the speed level, the segmental curve improves the efficiency to a certain degree. However, as the control system of urban rail transit requires for high density and large passenger flow, such system aboard has not fully made use of the advantages of communications-based train control system yet, and involves the following problems:
(1) The train in operation can only be positioned by means of track circuits or virtual sections at a poor accuracy, and a precise train-positioning has not been achieved yet;
(2) The tracking interval between trains is relatively longer, as a result, the movement authority is unable to increase the operation efficiency to a greatest extent;
(3) The expandability is poor, which is attributed to the tracking methods following speed level or segmental curve. In this case, if operation efficiency is required to be increased, a large number of wayside equipments have to be incorporated into the system, which results in exorbitant cost for upgrade.